As a conventional analog feedback amplifier, there is one which comprises an I-part comparator that takes the difference between the I-coordinate input signal of a baseband signal and a feedback signal, a Q-part comparator that takes the difference between the Q-coordinate input signal of the baseband signal and the feedback signal, a quadrature modulator that carries out quadrature modulation of the output signals of the IQ-part comparators and outputs an RF signal, a power amplifier that amplifies the RF output signal of the quadrature modulator, an attenuator that attenuates the RF output signal amplified by the power amplifier, and a quadrature demodulator that carries out quadrature demodulation of the RF output signal attenuated by the attenuator, supplies the I-coordinate signal of a baseband signal passing through the quadrature demodulation to the I-part comparator as the feedback signal, and supplies the Q-coordinate signal of the baseband signal passing through the quadrature demodulation to the Q-part comparator as the feedback signal (see the following Non-Patent Document 1).
In addition, as a conventional analog feedback amplifier, there is one which uses a polar coordinate system and performs an analog feedback in the same manner, and carries out band setting and follow-up control (see the following Patent Document 1).